Heretofore, it has been disclosed in the specifications of Japanese Patent Application Laid-Open No. Showa 62(1987)-25795, Japanese Patent Application Laid-Open No. Heisei 1(1989)-279944, Japanese Patent Application Laid-Open No. Heisei 2(1990)-209938, Japanese Patent Application Laid-Open No. Heisei 2(1990)-219843, Japanese Patent Application Laid-Open No. Heisei 3(1991)-126744, and Japanese Patent Application Laid-Open No. Heisei 4(1992)-269893 that compositions having a good balance between strength, toughness, heat resistance, chemical resistance, and processability in molding can be obtained by melt blending a styrenic polymer having the syndiotactic configuration (hereinafter, occasionally referred to as SPS), a polyamide resin, and a compatibilizer for SPS and a polyamide as the main components of the compositions. By taking advantage of these excellent properties, practical application to products which require strength and heat resistance, such as electric and electronic parts, automobile parts, mechanical parts, and parts of industrial products, is under examination.
However, the above resin composition has a problem that the resistance to degradation by oxidation at a high temperature for a long time, i.e. the resistance to heat aging, is not sufficient although the resin compositions have the above excellent characteristics. Therefore, improvement in the resistance to heat aging for a long time has strongly been desired in order to increase reliability of the parts described above.
For solving the above problem, addition of a phenolic antioxidant (Japanese Patent Application Laid-Open No. Heisei 5(1993)-289290) and a combined use of a phenolic antioxidant and an antioxidant containing sulfur (Japanese Patent Application Laid-Open No. Heisei 6(1994)-384) have been proposed. However, sufficient increase in the resistance to heat aging is not achieved by these technologies. Addition of a combination of a copper compound and an iodine compound and addition of an amine antioxidant have also been proposed in order to increase the resistance to heat aging of a polyamide. Although the resistance to heat aging is increased to some extent by addition of these compounds, the obtained properties are not satisfactory. Moreover, the addition causes other problems that color of the molded products changes with time into yellow or brown, and that adverse effects of the copper compound arise to cause corrosion of extruders, molding machines, and the like.
On the other hand, a polyamide resin comprising a phenolic antioxidant and an antioxidant containing sulfur has been proposed. However, satisfactory results have not been obtained by using this technology, either.
Under the above circumstances, the present invention has an object of providing a polystyrenic resin composition which shows excellent resistance to heat aging so that decrease in physical properties or change in color are hardly caused even after exposure to a high temperature for a long time, has excellent toughness, rigidity, heat resistance, and chemical resistance, and can advantageously be used as a material for various types of industrial product.